The enzyme, p70S6 kinase (also known as p70S6K, p70S6K1, pS6K, S6K, S6K1) is a serine-threonine kinase and a member of the AGC family. It is a downstream effector of the phosphatidylinositol 3 kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway and p70S6 undergoes phosphorylation and activation in response to growth factors such as IGF-I, EGF, TGF-[alpha] and HGF.
Activation of p70S6K in turn phosphorylates Ribosomal protein S6 (RPS6) which promotes translation leading to an increase in protein synthesis in a cell. High levels of protein synthesis are required for cellular proliferation. It has also been shown that p70S6K has a necessary role in the mitotic cycle of a cell (Lane et al, Nature, 1993, 363(6425):170-2).
The kinase p70S6K has been shown to be constitutively activated in human tumour cells, leading to tumour cell proliferation. Inhibition of the p70S6K/mTOR pathway has been shown to lead to a decrease in tumour cell proliferation and an increase in tumour cell apoptosis (Pene et al (2002) Oncogene 21, 6587 and Le et al (2003) Oncogene 22, 484). Inhibition of p70S6K activity would therefore present an attractive approach for the treatment of cancer.
The mTOR/p70S6K pathway has been shown to be activated in renal cell carcinoma and is inhibited by CCI-779 (Robb, V. A.; Karbowniczek, M.; Klein-Szanto, A. J.; Henske, E. P. J Urol 2007, 177, 346-52). Furthermore, patients with gliobastoma multiforme whose tumours express high levels of phosphorylated p70S6K have been found to benefit from treatment with CCI-779 (Galanis et al. J Clin Oncol 2005, 23, 5294-304).
In addition, a significant linear association between time to disease progression and inhibition of p70S6K activity in peripheral blood mononuclear cells (PBMCs) following administration of the mTOR inhibitor CCI-779 has been reported for Renal Cell Carcinoma patients by Peralba et al [(2003) Clinical Cancer Research 9, 2887]. This indicates that activity of p70S6K is a driver of disease in this setting and that p70S6K activity can be potentially be used as a clinical biomarker.
The gene RPS6KB1 that codes for p70S6K, is localized to chromosomal region 17q23 and this region is amplified in Breast Cancer (Cancer Res. (1999) 59: 1408-1 1—Localization of pS6K to Chromosomal Region 17q23 and Determination of Its Amplification in Breast Cancer). This leads to over-expression of p70S6K protein and a statistically significant association between amplification and poor prognosis has been observed in breast cancer patients (Detecting activation of ribosomal protein S6 kinase by complementary DNA and tissue microarray analysis. J Natl Cancer Inst 2000; 92:1252-9).
Furthermore, Belletti et al published that S6K1 mediates survival and recurrence of Breast Cancer following surgery (Mol Oncol. 2014 May; 8(3):766-80).
P70S6K has a role in migration and invasion of ovarian cancer (p70 S6 kinase in the control of actin cytoskeleton dynamics and directed migration of ovarian cancer cells, Oncogene (2011), 1-13). In addition, it has been revealed that p70S6K has a role in promoting invasion, migration and metastasis of highly aggressive Triple-Negative Breast Cancer cells (Targeting p70S6K Prevented Lung Metastasis in a Breast Cancer Xenograft Model, Akar et al, Molecular Cancer Therapeutics (2010), 9 (5), 1180 and Hung et al, S6K1 promotes invasiveness of breast cancer cells in a model of metastasis of triple-negative breast cancer, Am. J. Transl. Res. 2014 Jul. 18; 6(4):361-76).
In addition, Lymphangioleiomyomatosis (LAM) is a disease typified by hyper-activation of the PI3K/Akt/mTOR/p70S6K axis due to mutation inactivation of the repressor complex, Tuberous Sclerosis Complex (TSC). LAM cells are also metastatic, giving rise to metastasis in the lung.
LAM is a rare destructive lung disease, almost exclusively of women, and is associated with the metastasis of tuberin-null cells (Taveira-DaSilva et al. (2006). Cancer Control. 2006; 13:276-285). Metastatic lesions develop in distant organs including lungs, kidney and lymph nodes, representing a severe and debilitating disease burden.
LAM occurs either sporadically or as a manifestation of Tuberous Sclerosis Complex (TSC), a dominant autosomal inherited disorder (Expert review on http://www.orpha.net). LAM and TSC disorders are characterized by nullifying mutations in tumour suppressors TSC1 or TSC2 leading to hyper activation of mTOR and of S6K1. This in turn drives cell growth & proliferation of LAM cells (Holz et al. (2014), Cell Cycle 2014; 13:371-382).
S6K1 is also known to promote metastasis in other cancers: breast (Akar et al. (2010), Mol Cancer Ther; 9(5) May 2010) and ovarian (Wong et al. (2011), Oncogene (2011) 30, 2420-2432). Due to the reliance of LAM cells on S6K1, and of the likely role of S6K1 in the metastatic process, it is anticipated that an S6K1 inhibitor will have disease-modifying properties for LAM.
Sporadic LAM has a prevalence of approx. 1 in 125,000 births whereas Pulmonary LAM, arising from TSC, has a prevalence of approx. 1 in 15,000 births (figures from internet rare disease database, http://www.orpha.net). No approved therapies exist for LAM and hence LAM is currently classified as an orphan disease.
Given that p70S6K promotes translation, it is known that p70S6K has a crucial role in the pathology of diseases that rely on excessive protein synthesis (for example, Fragile X Syndrome, Genetic Removal of p70 S6 Kinase 1 Corrects Molecular, Synaptic, and Behavioral Phenotypes in Fragile X Syndrome Mice. Klann et al, Neuron, Volume 76, Issue 2, p325-337, 18 Oct. 2012). Furthermore, p70S6K has a role in the pathology of cancers involving synthesis of oncogenic proteins such as c-Myc e.g. pancreatic cancer (The mTORC1/S6K1 Pathway Regulates Glutamine Metabolism through the eIF4B Dependent Control of c-Myc Translation, Blenis et al, Current Biology, Volume 24, Issue 19, p2274-2280, 6 Oct. 2014). For treatment of these conditions it would be advantageous to use an orally bioavailable p70S6K inhibitor to correct the excessive protein synthesis.
P70S6K has been implicated in the pathology of a number of cancers of the brain. Such conditions include, but are not limited to:                Brain metastases arising from cancers elsewhere in the body, for example brain metastases arising from a breast cancer such as Triple-Negative Breast Cancer (Distant metastasis in triple-negative breast cancer. Neoplasma 2013; 60: 290-294)        Brain metastases from metastatic breast cancer (Central nervous system or brain metastases traditionally occur in 10-16% of metastatic breast cancer patients and are associated with a dismal prognosis—see Breast Dis. 2006-2007; 26:139-47.)        Gliomas and Glioblastomas (S6K1 Plays a Key Role in Glial Transformation, Cancer Research (2008), 68(16), 6516-6523)        
Furthermore, a p70S6K inhibitor may be particularly useful for treating the following cancers which are reliant on p70S6K signaling:                Bladder cancer        Breast cancer        Colo-rectal cancer (CRC)        Diffuse large B-cell lymphomas (DLBCL)        Gallbladder cancer        Head and Neck cancers        Hepatocellular carcinoma        Human Olfactory Neuroblastoma        Leukaemias        Lymphomas        Nasopharyngeal carcinoma        Neuroendocrine cancer        Non-Small Cell Lung Cancer (NSCLC)        Ovarian cancer        Pancreatic cancer        Pheochromocytoma        Renal Cell Carcinoma (RCC)        Squamous cell carcinoma        Metastases, for example bone metastases and lung metastases        
P70S6K also has a crucial role in the pathology of a number of neurodevelopmental diseases (many referenced in The Autistic Neuron: Troubled Translation?. Bear et al, Cell 135, Oct. 31, 2008). In particular, these diseases are caused by the excessive protein synthesis that is driven by P70S6K. Such conditions include, but are not limited to:                Fragile X Syndrome, a rare neuro-developmental disease caused by excessive levels of p70S6K activity        Autism and Autism Spectrum Disorders        Fragile X-associated tremor/ataxia syndrome (FXTAS)        Angleman's syndrome        Tuberous sclerosis        PTEN hamartoma syndrome        MECP2 duplication syndrome        Neurofibromatosis        Alzheimer's Disease (refer to (1) Oddo et al, Reducing Ribosomal Protein S6 Kinase 1 Expression Improves Spatial Memory and Synaptic Plasticity in a Mouse Model of Alzheimer's Disease, The Journal of Neuroscience, Oct. 14, 2015, 35(41):14042-14056 and (2) Genetic reduction of mammalian target of rapamycin ameliorates Alzheimer's disease-like cognitive and pathological deficits by restoring hippocampal gene expression signature, Journal of Neuroscience (2014), 34(23), 7988-7998)        Down Syndrome (mTOR Hyperactivation in Down Syndrome Hippocampus Appears Early During Development, Journal of Neuropathology & Experimental Neurology (2014), 73(7), 671-683)        
PTEN Hamartoma Syndrome
PTEN hamartoma tumour syndrome (PHTS) encompasses four major clinically distinct syndromes associated with germline mutations in the tumour suppressor PTEN. These allelic disorders, Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, Proteus syndrome, and Proteus-like syndrome are associated with unregulated cellular proliferation leading to the formation of hamartomas (benign and malignant tumours of the thyroid, breast, and endometrium) (Genetics in Medicine (2009) 11, 687-694). The absence of PTEN leads to loss of down-regulation of phosphorylated Akt which in turn allows for unchecked survival, growth and proliferation of the cells in question. As S6K1 is a key effector of Akt, an S6K1 inhibitor may have utility in controlling the growth of the cancer. Prevalence of PHTS is currently unknown.
Neurofibromatosis Type 1
Neurofibromatosis type 1 is a condition characterized by changes in skin colouring (pigmentation) and the growth of tumours along nerves in the skin, brain, and other parts of the body. The signs and symptoms of this condition vary widely among affected people. Most adults with neurofibromatosis type 1 develop neurofibromas, which are noncancerous (benign) tumours that are usually located on or just under the skin. These tumours may also occur in nerves near the spinal cord or along nerves elsewhere in the body. Some people with neurofibromatosis type 1 develop cancerous tumours that grow along nerves. These tumours, which usually develop in adolescence or adulthood, are called malignant peripheral nerve sheath tumours. People with neurofibromatosis type 1 also have an increased risk of developing other cancers, including brain tumours and cancer of blood-forming tissue (leukemia).
Neurofibromatosis type 1 occurs in 1 in 3,000 to 4,000 people worldwide and currently surgery is the main treatment option; it is classed as an orphan disease as no targeted therapies exist (http://ghr.nlm.nih.gov/condition/neurofibromatosis-type-1)
Mutations in the NF1 gene cause neurofibromatosis type 1. The NF1 gene provides instructions for making neurofibromin protein. This protein is produced in many cells, including nerve cells and specialized cells surrounding nerves (oligodendrocytes and Schwann cells). Neurofibromin acts as a tumour suppressor. Mutations in the NF1 gene lead to the production of a non-functional version of neurofibromin that cannot regulate cell growth and division. As a result, tumours such as neurofibromas can form along nerves throughout the body. An S6K1 inhibitor may control growth of cells expressing mutated NF1 gene by dampening production of neurofibromin protein and other proteins essential to growth of the tumour.
Role of P70S6 in Neurological Diseases
P70S6K also has a crucial role in the pathology of a number of neurodevelopmental diseases (many referenced in The Autistic Neuron: Troubled Translation?. Bear et al, Cell 135, Oct. 31, 2008). In particular, these diseases are caused by the excessive protein synthesis that is driven by P70S6K.
It is well known that precise translation control (protein synthesis) is absolutely required for neurological processes of the brain such as long-lasting synaptic plasticity and the formation of long-term memory. Moreover, alterations in translational control are a common pathophysiological feature of human neurological disorders, including developmental disorders, neuropsychiatric disorders, and neurodegenerative diseases. Furthermore, it is known that translational control mechanisms are susceptible to modification by small molecules that penetrate the brain (Klann and Santini, Dysregulated mTORC1-dependent translational control: from brain disorders to psychoactive drugs, Front. Behav. Neurosci., 8 Nov. 2011, doi: 10.3389/fnbeh.2011.00076).
S6K1 is well known as a master regulator of protein biosynthesis via its role in translation initiation as well as phosphorylation and activation of various substrates that drive protein production (eIF4B, PDCD4, SKAR, eEF2K, RPS6—for review refer to Ma and Blenis, Nature Reviews Molecular Cell Biology 10, 307-318 (May 2009), doi:10.1038/nrm2672).
The following disorders are typified by underlying aberrations in regulation of protein translation which is linked to the pathologies observed. An S6K1 inhibitor, which acts by reducing excessive protein translation may therefore have utility as a therapy in such disorders.
It is possible to classify certain disorders into sub-groups: (1) Neurodevelopmental Disorders (2) Neurodegenerative Diseases. Within each sub-class the disorders are linked by common themes:
1. Neurodevelopmental Disorders
Neurodevelopmental disorders are defined as diseases caused by abnormal development of the brain during the first two decades of life. It is possible to define a subgroup of these disorders that are characterized by single-gene mutations. A common molecular abnormality in several of these disorders is loss-of-function mutations and/or deletion of genes that encode proteins that normally repress mTORC1 signaling pathway. These disorders are listed below.
Fragile X Syndrome
Fragile X syndrome is a genetic condition that gives rise to a range of developmental problems including learning disabilities and cognitive impairment. Usually, males are more severely affected by this disorder than females, owing to the fact that the condition is inherited via the X-chromosome. Affected individuals usually have delayed development of speech and language by age 2. Most males with fragile X syndrome have mild to moderate intellectual disability, while about one-third of affected females are intellectually disabled. Children with fragile X syndrome may also have anxiety and hyperactive behavior such as fidgeting or impulsive actions. They may have attention deficit disorder (ADD), which includes an impaired ability to maintain attention and difficulty focusing on specific tasks. About one-third of individuals with fragile X syndrome have features of autism spectrum disorders that affect communication and social interaction. Seizures occur in about 15 percent of males and about 5 percent of females with fragile X syndrome. Most males and about half of females with fragile X syndrome have characteristic physical features that become more apparent with age. These features include a long and narrow face, large ears, a prominent jaw and forehead, unusually flexible fingers, flat feet, and in males, enlarged testicles (macroorchidism) after puberty. Fragile X syndrome occurs in approximately 1 in 4,000 males and 1 in 8,000 females.
Mutations in the FMR1 gene cause fragile X syndrome. The FMR1 gene provides instructions for making a protein called fragile X mental retardation 1 protein, or FMRP. This protein helps regulate the production of other proteins and plays a role in the development of synapses, which are specialized connections between nerve cells. Synapses are critical for relaying nerve impulses.
Nearly all cases of fragile X syndrome are caused by a mutation in which a DNA segment, known as the CGG triplet repeat, is expanded within the FMR1 gene. Normally, this DNA segment is repeated in the range between 5 and 44 times (more commonly either 29 or 30 times). In people with fragile X syndrome, however, the CGG segment is repeated more than 200 times. The abnormally expanded CGG segment turns off (silences) the FMR1 gene, which prevents the gene from producing FMRP.
FMRP is a repressor of protein translation. In the case of FXS patients, who either experience a loss or shortage of FMRP, there is no repression of translation, leading to excessive production of an array proteins normally controlled by FMRP. A number of these proteins are expressed in the neurons and control synaptic plasticity (memory formation, learning, ability to store information). Lack of control of production of these proteins leads to the neuropathological state observed in FXS patients. Klann et al published that S6K1 has a central role in the excessive translation of these proteins and that genetic knock-out of S6K1 resulted in correction of phenotypes in the mouse model of FXS (Genetic Removal of p70 S6 Kinase 1 Corrects Molecular, Synaptic, and Behavioral Phenotypes in Fragile X Syndrome Mice. Neuron 76, 325-337, 2012). It has been determined that S6K1 inhibitors described herein also have the ability to dampen protein synthesis in the neurons, leading to correction of aberrant phenotypes in a mouse model of FXS.
Furthermore, Tassone et al (Genes, Brain and Behavior (2012), doi: 10.1111/j.1601-183X.2012.00768.x) published that lymphocytes isolated from the blood of human FXS patients exhibited higher levels of phosphorylated (activated) p70S6K and also higher levels of phosphorylated RPS6, the direct substrate of S6K1. This confirms that p70S6K is more highly activated in human FXS patients and supports the notion of inhibiting p70S6K activity in order to correct the disease. In addition, this represents a possible clinical biomarker so as to assess the pharmacodynamics effect of the p70S6K inhibitor in the clinic.
Fragile X-associated Tremor/Ataxia Syndrome (FXTAS)
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a rare neurodegenerative disorder characterized by adult-onset progressive intention tremor and gait ataxia. It is an X-linked genetic disorder and as such, the disease primarily affects males (Orphanet rare disease database, http://www.orpha.net/consor/cgi-bin/index.php?Ing=EN)
Prevalence is estimated at 1-9 in 100,000 individuals. The age of onset of tremor and/or ataxia in males is about 60 years. The clinical presentation is variable with dominant manifestations including: intention tremor, progressive cerebellar gait ataxia, frontal executive dysfunction, cognitive decline, peripheral neuropathy, and dysautonomia. Other signs include mild Parkinsonism and psychiatric manifestations (depression, anxiety, agitation) with possible progression to dementia. Carrier females generally have less severe manifestations than males but also have an increased risk of primary ovarian insufficiency, chronic muscle pain, and hypothyroidism. FXTAS is caused by a CGG trinucleotide repeat expansion (55-200 repeats) in the permutation range of the FMR1 gene. There is no specific treatment for FXTAS that targets the underlying pathological mechanism; FXTAS is therefore classed as an orphan disease. The CGG trinucleotide repeat expansion often leads to reduced levels of FMRP protein, a repressor of protein translation. This leads to excessive protein translation which may be counter-acted by use of an S6K1 inhibitor.
Autism and Autism Spectrum Disorders
Autism spectrum disorder (ASD) and autism are terms for a group of complex disorders of brain development. The disorders are characterized by difficulties in social interaction, verbal and nonverbal communication and repetitive behaviours. A publication in 2013 titled the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) brought together all autism disorders into one umbrella diagnosis of ASD. Previously, they were recognized as distinct subtypes, including autistic disorder, childhood disintegrative disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS) and Asperger syndrome. The U.S. Centers for Disease Control and Prevention (CDC) identify around 1 in 68 American children as on the autism spectrum. Studies also show that autism is four to five times more common among boys than girls. An estimated 1 out of 42 boys and 1 in 189 girls are diagnosed with autism in the United States. Overall, ASD affects over 3 million individuals in the U.S. and tens of millions worldwide (Autism Speaks website, http://www.autismspeaks.org/). Moreover, government autism statistics suggest that prevalence rates are on the increase. Fragile X syndrome (FXS) is the most common inherited cause of intellectual disabilities and the most common known cause of autism worldwide (Penagarikano et al (2007). The pathophysiology of Fragile X Syndrome. Annu. Rev. Genomics Hum. Genet. 8, 109-129). This causative link between FXS and autism indicates that an S6K1 inhibitor that exhibits efficacy in treating FXS may also be useful in treatment of autism and ASDs.
Angelman's Syndrome
Angelman's syndrome (AS) is a neurogenetic disorder that is usually diagnosed in infants and is characterized by developmental delay, severe intellectual disability, absent speech, exuberant behaviour with happy demeanor, motor impairment, and epilepsy. AS is caused by deficient UBE3A gene expression that may be caused by various abnormalities of chromosome 15 (Dan, B., Angelman syndrome: Current understanding and research prospects. Epilepsia, 2009. 50(11): p. 2331-2339). Although not precisely known, prevalence of AS among children and young adults is between 1/10,000 and 1/20,000 defining AS as a rare disease. Mutations in the E3 ubiquitin ligase UBE3A have been identified in AS, suggesting that ubiquitin-dependent protein turnover may be impaired in this disorder, possibly leading to elevated synaptic protein levels (Jiang and Beaudet, 2004). An S6K1 kinase inhibitor would exert its effect by reducing translation of synaptic protein levels.
Tuberous Sclerosis Complex
Tuberous sclerosis complex is a genetic disorder characterized by the growth of numerous noncancerous (benign) tumours in many parts of the body. These tumours can occur in the skin, brain, kidneys, and other organs, in some cases leading to significant health problems. Tuberous sclerosis complex also causes developmental problems, and the signs and symptoms of the condition vary from person to person.
Tuberous sclerosis complex often affects the brain, causing seizures, behavioral problems such as hyperactivity and aggression, and intellectual disability or learning problems. Some affected children have the characteristic features of autism, a developmental disorder that affects communication and social interaction. Benign brain tumours can also develop in people with tuberous sclerosis complex; these tumours can cause serious or life-threatening complications. Tuberous sclerosis complex affects about 1 in 6,000 people (http://ghr.nlm.nih.gov/condition/tuberous-sclerosis-complex)
Mutations in the TSC1 or TSC2 gene can cause tuberous sclerosis complex. The TSC1 and TSC2 genes provide instructions for making the proteins hamartin and tuberin, respectively. These proteins are involved in the signaling network of the PI3K pathway and act as tumour suppressors, inhibiting the activation of mTOR via Rheb-GTP. When TSC1 or TSC2 are mutated this leads to loss of tumour suppressor function, leading to mTOR hyper-activation.
Importantly, the mTORC1 inhibitor rapamycin has been shown to be effective in ameliorating learning and memory deficits in TSC2 heterozygous knockout mice (Ehninger et al., 2008b), suggesting that uncontrolled mTORC1 signaling is a core molecular mechanism involved in the behavioral abnormalities.
One of the functional effectors of mTOR is S6K1; therefore, inhibiting S6K1 function may have ameliorative effects in the disease
MECP2 Duplication Syndrome
MECP2 duplication syndrome is a genetic condition that is inherited in an X-linked pattern and occurs almost exclusively in males. It is characterized by moderate to severe intellectual disability. Most people with this condition also have weak muscle tone in infancy, feeding difficulties, poor or absent speech, seizures that may not improve with treatment or muscle stiffness (spasticity). Individuals with MECP2 duplication syndrome have delayed development of motor skills such as sitting and walking. Many individuals with MECP2 duplication syndrome have recurrent respiratory tract infections. These respiratory infections are a major cause of death in affected individuals, with almost half succumbing by age 25. The prevalence of MECP2 duplication syndrome is unknown;
approximately 120 affected individuals have been reported in the scientific literature. MECP2 duplication syndrome arises due to a duplication of the MECP2 gene which leads to excessive production of MeCP2 protein in the brain. MeCP2 is a regulator of expression of other genes. Whilst MeCP2 is critical for normal brain function, an excess can lead to abnormal regulation of the target genes (http://ghr.nlm.nih.gov/condition/mecp2-duplication-syndrome). An S6K1 inhibitor may reduce production of MeCP2 protein via global dampening of translation and may have utility as therapeutic intervention in this disease.
Down Syndrome
Down syndrome (DS) or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21 (Patterson, D (July 2009). “Molecular genetic analysis of Down syndrome.”. Human Genetics 126 (1): 195-214). It is typically associated with physical growth delays, characteristic facial features, and mild to moderate intellectual disability. DS is the most common chromosome abnormality in humans, occurring in about one per 1000 babies born each year (Weijerman, M E; de Winter, J P (December 2010). “Clinical practice. The care of children with Down syndrome.”. European journal of pediatrics 169 (12): 1445-52).
Recent publications have identified that mTOR hyperactivation plays a role in DS in the early stages of development. In control (non-DS) hippocampi phosphorylated S6 was only detected prenatally; it became undetectable 2 months postnatally. Conversely, for DS patients, phosphorylated S6 and phosphorylated S6 kinase were detected prenatally and persisted throughout postnatal development. This was linked to increased expression of phosphorylated S6 protein (RPS6), phosphorylated p70S6K, phosphorylated eukaryotic initiation factor 4E binding protein 1, and phosphorylated mTOR in DS hippocampus compared with controls (J Neuropathol Exp Neurol. 2014 July; 73(7):671-83). Furthermore, it has been suggested that mTOR inhibitors such as Rapamycin or other Rapalogs may be of utility in treating Cognitive Deficits associated with DS (CNS Neurol Disord Drug Targets. 2014 February;13(1):34-40). As S6K1 controls phosphorylation and activation of S6 protein, an S6K1 inhibitor may be of therapeutic utility in counter-acting the hyper-activated mTOR signaling in DS patients.
2. Neurodeqenerative Diseases
Alzheimer's Disease
The clinical symptoms of Alzheimer disease (AD) include a gradual memory loss and subsequent dementia, and neuropathological deposition of senile plaques and neurofibrillary tangles. AD accounts for 60% to 70% of cases of dementia (Burns, A; Lliffe, S (5 Feb. 2009). “Alzheimer's disease.”BMJ (Clinical research ed.) 338: b158). It is a devastating and relatively widespread disease—as of 2010, there were between 21 and 35 million people worldwide with AD (“Survival in dementia and predictors of mortality: a review”. International journal of geriatric psychiatry 28 (11): 1109-24).
At the molecular level, AD is associated with (1) the progressive accumulation of amyloid β-peptides (Aβ) in the form of extracellular amyloid plaques in the human brain and (2) tau hyperphosphorylation. Recent publications have implicated the PI3K/mTOR signaling pathway in the pathogenesis of the disease. For example, genetic knock-out of mTOR protein in Tg2576 mice, a widely used animal model of AD, was found to suppress amyloid-β deposits and rescue memory deficits in the animals (J Neurosci. 2014 Jun. 4; 34(23):7988-98). Furthermore, testing of post-mortem brain tissue from human AD patients highlighted that alteration of mTOR signaling and autophagy occurs at early stages of AD, leading to a significant increase of Aβ (1-42) levels and hyper-activation of the PI3K/Akt/mTOR pathway (J Neurochem. 2015 Jan. 27). The expression level of S6K1, the mTOR downstream target, was increased in these samples suggesting that a therapeutic intervention by an S6K1 inhibitor may be of utility to control synthesis of amyloid β protein and to dampen signaling from mTOR. Furthermore, increased levels of phosphorylated mTOR and S6K1 were also found in some of the brain areas affected in AD, such as cortex, of double APP/PS1 transgenic mice, a model of AD (Lafay-Chebassier et al., 2005).
In addition, Oddo et al (Reducing Ribosomal Protein S6 Kinase 1 Expression Improves Spatial Memory and Synaptic Plasticity in a Mouse Model of Alzheimer's Disease, The Journal of Neuroscience, Oct. 14, 2015, 35(41):14042-14056) published data that supports the following conclusions: (1) S6K1 activity is upregulated in the brains of AD patients (2) in a mouse model of AD, S6K1 activity in brain is also higher than control (3) Genetic reduction of S6K1 in the AD model mouse (via haplodeficiency) (A) improved synaptic plasticity and spatial memory deficits, and (B) reduced accumulation of Amyloid-B (AB) and phospho-tau/total tau levels, the key neuropathological hallmarks of AD. This validation gives credence to the hypothesis that manipulation of S6K1 activity via a small molecule S6K1 inhibitor could be a valid therapeutic approach in AD.
Huntington's Disease
Huntington's disease is an inherited, progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition); there are two forms of the disease: (1) adult-onset Huntington's disease, the most common form of this disorder, which usually appears in a person's thirties or forties and (2) Juvenile-onset Huntington disease, which is less common and begins in childhood or adolescence. In both forms the disease is progressive with affected individuals usually living for only 10 to 15 years after signs and symptoms appear. Huntington's disease affects an estimated 3 to 7 people per 100,000 of European ancestry.
Huntington disease is caused by Mutations in the HTT gene which leads to production of an abnormally long version of the huntingtin protein. The elongated protein is cut into smaller, toxic fragments that bind together and accumulate in neurons, disrupting the normal functions of these cells. The dysfunction and eventual death of neurons in certain areas of the brain underlie the signs and symptoms of Huntington disease. Recent publications have shown that mutant Htt contributes to the pathogenesis of HD by enhancing mTORC1 activity (Sci. Signal., 28 Oct. 2014, Vol. 7, Issue 349, p. ra103).
One of the functional effectors of mTOR signaling is S6K1; therefore, inhibiting S6K1 function may have ameliorative effects in the disease. In addition, inhibiting S6K1 may limit the production of huntingtin protein via dampening of global protein translation.
Parkinson's Disease
Parkinson's disease (PD) is a progressive neurodegenerative condition resulting from the death of the dopamine-containing cells of the substantia nigra. People with PD classically present with the symptoms and signs associated with parkinsonism, namely bradykinesia, rigidity and rest tremor. PD is a common, chronic, progressive neurological condition, estimated to affect 100-180 people per 100,000 of the population (between 6 and 11 people per 6000 of the general population in the UK) and has an annual incidence of 4-20 per 100,000. There is a rising prevalence with age and a higher prevalence and incidence of PD in males (https://www.nice.org.uk/guidance/cg035/chapter/introduction).
Whilst PD traditionally has been considered a non-genetic disorder, at least 5% of people are now known to have forms of the disease that occur because of a mutation of one of several specific genes. Mutations in specific genes have been conclusively shown to cause PD. These genes code for alpha-synuclein (SNCA), parkin (PRKN), leucine-rich repeat kinase 2 (LRRK2 or dardarin), PTEN-induced putative kinase 1 (PINK1), DJ-1 and ATP13A2 (Lesage S, Brice A; Brice (April 2009). “Parkinson's disease: from monogenic forms to genetic susceptibility factors”. Hum. Mol. Genet. 18 (R1): R48-59).
Recent studies addressing the mechanism of neurodegeneration in PD demonstrate the involvement of the mTORC1 signaling pathway in the survival mechanism of dopaminergic neurons. In vivo and in vitro studies show that degeneration induced by treatment with PD toxins, such as 6-OHDA and MPTP, leads to upregulation of RTP801, a protein encoded by a RTP801 stress-responsive gene, which in turn reduces mTOR kinase activity. It has been proposed that the molecular mechanism, linking high levels of RTP801 to mTORC1 inhibition and neurodegeneration involves TSC2 and Akt (Deyoung et al., 2008; Malagelada et al., 2008). Either genetic manipulations that interfere with TSC2 or increase the expression of a constitutively active form of Akt protected against the PD toxins and prevented the increase in RTP801 (Malagelada et al., 2008). However, rapamycin was reported as neuroprotective agent both in cell culture and in a MPTP mouse model (mouse model of PD). It was proposed that rapamycin may enhance Akt activity through inhibition of mTORC1-dependent activation of S6K1 and the subsequent reduction of phospho-IRS-1, which is a scaffold protein involved in the activation of PI3K and Akt (Shah et al., 2004). It therefore may also be the case that an inhibitor of S6K1 (a main effector of mTOR) will uncouple the same negative feedback loop to IRS-1, leading to activation of Akt and increased survival in the neurons of PD patients. An S6K1 inhibitor may therefore exhibit therapeutic effects when dosed to a PD patient.
For treatment of the above diseases it would be advantageous to use an orally bioavailable P70S6K inhibitor with properties allowing penetration of the brain in sufficient concentrations to achieve efficacy.
It would therefore be beneficial to develop compounds that have the ability to inhibit p70S6 kinase.